Available dashboard filters are persisted

AT:

• The setting which filters are available for a dashboard is persisted in the backend
• For that, the PUT /api/dashboard/:id endpoint is extended to include a new field:

{
  "availableFilters": [
    {"type": "state"} // or "startDate" or "endDate"
  ]
}

• the same field is added to the create dashboard endpoint
• the GET /api/dashboard/:id returns the new availableFilters field unchanged
• this change is documented in confluence